Murine pulmonary surfactant SP-A gene: cloning, sequence, and transcriptional activity

SP-A is an abundant pulmonary surfactant-associated protein whose expression is controlled in a cell- and developmental-specific manner. To analyze regulation of SP-A gene expression, the murine SP-A gene was cloned and sequenced. The murine DBA/2J gene was approximately 4.6 kb in length comprised of six exons and five introns. Three mRNAs of 3.0, 1.7, and 0.9 kb were detected by Northern blot analysis of murine lung mRNA. Expression of the SP-A mRNAs was first detected at day 15 of gestation and increased dramatically before birth. A single SP-A gene was detected in the DBA/2J mouse genome. SP-A mRNA was detected in lung but not in the gastrointestinal tract, kidney, brain, liver, or heart and was detected by in situ hybridization in bronchial and alveolar cells of the murine lung. Primer extension analysis with a primer to exon three revealed two extension products differing by 9 bp in length, suggesting two closely juxtaposed transcription initiation sites. Chimeric gene(s) containing 1.8 kb of 5' SP-A sequences and the bacterial chloramphenicol acetyltransferase gene were expressed in pulmonary adenocarcinoma cells and in HeLa cells. Expression of the murine SP-A gene is partially controlled by non-cell-selective transcriptionally active sequences.